【International Papers】Hole diffusion effect on the minority trap detection and non-ideal behavior of NiO/β-Ga₂O₃ heterojunction

      Researchers from the Sejong University , South Korea have published a dissertation titled "Hole diffusion effect on the minority trap detection and non-ideal behavior of NiO/β-Ga₂O₃ heterojunction " in Applied Physics Letters.

ABSTRACT

      A NiO/β-Ga₂O₃ heterojunction was fabricated by sputtering a highly p-doped NiO layer onto β-Ga₂O₃. This heterojunction showed a low leakage current and a high turn-on voltage (V_on) compared to a Ni/β-Ga₂O₃ Schottky barrier diode. The extracted V_on from the NiO/β-Ga₂O₃ heterojunction's forward current–voltage characteristics was ∼1.64 V, which was lower than the extracted built-in potential voltage (V_bi) obtained from the capacitance–voltage curve. To explain this difference, deep level transient spectroscopy and Laplace-deep level transient spectroscopy were employed to study majority and minority traps in β-Ga₂O₃ films. A minority trap was detected near the surface of β-Ga₂O₃ under a reverse bias of −1 V but was not observed at −4 V, indicating its dependence on hole injection density. Using Silvaco TCAD, the hole diffusion length from P⁺-NiO to β-Ga₂O₃ was determined to be 0.15 μm in equilibrium, which is increased with increasing forward voltage. This finding explained why the trap level was not detected at a large reverse bias. Moreover, hole diffusion from NiO into β-Ga₂O₃ significantly affected the β-Ga₂O₃ surface band bending and impacted transport mechanisms. It was noted that the energy difference between the conduction band minimum (CBM) of β-Ga₂O₃ and the valence band maximum (VBM) of NiO was reduced to 1.60 eV, which closely matched the extracted Von value. This supported the dominance of direct band-to-band tunneling of electrons from the CBM of β-Ga₂O₃ to the VBM of NiO under forward bias voltage.

FIG. 1 (a) Schematic of Ni/β-Ga₂O₃ SBD and NiO/β-Ga₂O₃ HJ devices, (b) SEM image of NiO/β-Ga₂O₃ HJ, (c) semi-logarithmic J–V characteristics of NiO/β-Ga₂O₃ SBD and NiO/β-Ga₂O₃ HJ, and the inset shows the extracted ideality factor vs forward bias for both devices and (d) C–V characteristics of both devices and the inset is the related 1/C² vs reverse bias curves.

FIG. 2. DLTS spectra of Ni/β-Ga₂O₃ SBD and NiO/β-Ga₂O₃ HJ at (a) V_R = −1 V, (c) V_R = −4V, and (b) and (d) Arrhenius plots of detected traps at V_R = −1 V and V_R = −4 V, respectively, and the majority and minority trap levels reported previously for comparison purposes.

Paper Link：https://doi.org/10.1063/5.0180427